ATAG is a Dutch heating manufacturer founded in 1930. Known for producing highly efficient, premium condensing boilers, their IC and IS combi and system boiler ranges are popular in the UK among those seeking top-tier efficiency. ATAG fault codes use a mix of numeric and alphanumeric codes.
ATAG Boiler Fault Codes
All ATAG Fault Codes 38
| Code | Fault | Severity | Type | View guide |
|---|---|---|---|---|
| 10 | Flow NTC Fault Flow sensor faulty. | Medium | Engineer | View Guide |
| 108 | Low Water Pressure — Refill Required On ATAG IC/IS boilers, code 108 indicates the system pressure needs filling (below 0.5 bar).… | Low | DIY Check | View Guide |
| 11 | Return NTC Fault Return sensor faulty. | Medium | Engineer | View Guide |
| 110 | Safety Temperature Exceeded / Overheat On ATAG IC/IS boilers, code 110 indicates the safety temperature limit has been exceeded. Also… | High | Engineer | View Guide |
| 111 | Pressure Too High The system water pressure has exceeded the maximum safe limit on ATAG boilers. | Medium | Engineer | View Guide |
| 12 | DHW NTC Fault Hot water sensor faulty. | Medium | Engineer | View Guide |
| 129 | Fan Not Starting The boiler fan is not starting up correctly, preventing safe ignition. | High | Engineer | View Guide |
| 133 | Ignition Failure — No Flame After 5 Attempts The most common ATAG fault code. The boiler has failed to ignite after 5 attempts.… | Medium | DIY Check | View Guide |
| 15 | Fan Fault Fan not running. | High | Engineer | View Guide |
| 151 | Fan Speed Error / Control Unit Fault The fan is not achieving the correct speed, or the control unit has detected a… | High | Engineer | View Guide |
| 154 | Return Temperature Higher Than Flow / Rapid Rise The return temperature is greater than the flow temperature, or the flow temperature is rising… | Medium | Engineer | View Guide |
| 16 | APS Fault Air pressure switch fault. | High | Engineer | View Guide |
| 17 | Gas Valve Fault Gas valve not responding. | High | Engineer | View Guide |
| 18 | Ignition Failure Failed to ignite. | High | Engineer | View Guide |
| 19 | Flame Lost Flame lost during operation. | High | Engineer | View Guide |
| 20 | Flow Sensor Error The heating flow temperature sensor has a fault. | Medium | Engineer | View Guide |
| 21 | Overheat Safety thermostat activated. | High | Engineer | View Guide |
| 22 | Low Pressure Pressure too low. | Low | DIY Check | View Guide |
| 23 | Pump Fault Pump not running. | High | Engineer | View Guide |
| 24 | Rapid Temperature Rise Flow temp rising too fast. | High | Engineer | View Guide |
| 25 | Condensate Blocked Condensate drain blocked. | Medium | DIY Check | View Guide |
| 26 | Diverter Fault Valve stuck. | Medium | Engineer | View Guide |
| 27 | PCB Fault Internal PCB error. | High | Engineer | View Guide |
| 28 | Combustion Fault Air/gas outside limits. | High | Engineer | View Guide |
| 29 | Pressure Sensor Fault Sensor faulty. | Medium | Engineer | View Guide |
| 30 | Frost Protection Frost protection active. | Medium | DIY Check | View Guide |
| 303 | PCB Error The main Printed Circuit Board has detected an internal fault. | High | Engineer | View Guide |
| 304 | Too Many Resets The boiler has been reset too many times and has entered a protective lockout. | Medium | DIY Check | View Guide |
| 31 | eBUS Fault Communication fault. | Medium | Engineer | View Guide |
| 32 | Flue Gas Overheat Flue gas too hot. | High | Engineer | View Guide |
| 33 | Outdoor Sensor Outdoor sensor faulty. | Low | Engineer | View Guide |
| 34 | Mains Voltage Voltage outside range. | Medium | Engineer | View Guide |
| 35 | EEPROM Error PCB memory error. | High | Engineer | View Guide |
| 36 | Flame After Shutdown Flame with gas off. | High | Engineer | View Guide |
| 40 | Return Sensor Error The heating return temperature sensor has a fault. | Medium | Engineer | View Guide |
| 501 | No Flame Detected No flame signal detected during operation. Separate from code 133 (ignition failure) — this may… | Medium | Engineer | View Guide |
| 61 | Bus Communication Error There is a communication fault on the bus between the boiler and external controls. | Medium | Engineer | View Guide |
| 78 | Water Pressure Out of Range The system water pressure is either too high or too low on ATAG boilers. | Low | DIY Check | View Guide |